1. Field of the Invention
The present invention relates to method of and apparatus for printing a cassette accommodating a recording medium or a cassette accommodating case and a cassette accommodating a recording medium and particularly to an intaglio printing method and apparatus of the cassette accommodating the recording medium and the cassette accommodating case and the cassette accommodating the recording medium to be printed.
2. Background of the Invention
Some recording-medium housing cassettes, for example, tape cassettes and housing cases thereof, have on their surfaces write areas (so-called label areas) formed by direct printing with an ink on which letters and the like can be directly written with a writing instrument. A title of the cassette and the like can be directly written with the writing instrument on the label area formed by printing.
FIG. 1 shows an example of the recording-medium housing cassette having the label area, i.e., a tape cassette or a so-called audio compact cassette which is commercially available on the market. A tape cassette 1 includes a plastic cassette housing 2 in which a pair of hubs around which a magnetic tape is wound as the recording medium are rotatably accommodated. Insertion apertures 3a, 3b of hub driving shafts for magnetic tape traveling are formed through a substantially middle portion of the tape cassette 1. The cassette tape 1 has through its trapezoidal portion insertion apertures 4a, 4b of capstans for the magnetic-tape travelling and reference apertures 5a, 5b used for positioning the cassette in a recording and/or reproducing apparatus. These insertion apertures 3a, 3b, insertion apertures 4a, 4b and the reference apertures 5a, 5b are formed so as to pierce the tape cassette 1 in its thickness direction. Though not shown, a plurality of opening portions used for recording and/or reproducing an information signal on and/or from the magnetic tape are formed through a side surface corresponding to the trapezoidal portion of the tape cassette 1.
Reference numeral 6 depicts a print surface which is formed on a surface of the cassette housing by a so-called solid printing with the ink where letters and the like can be directly written. The user can write music selection titles and so on on the print surface 6 with a pen.
A so-called pad printing is typically considered as one of methods of such printing on the tape cassette 1.
A printing method based on the pad printing will be briefly described with reference to FIGS. 2A through 2F.
As shown in FIG. 2A, an ink 11 is coated on a plate, i.e., an intaglio plate 10. Subsequently, as shown in FIG. 2B, extra ink is removed by a blade 12 and only the ink 11 of a necessary amount is left in a concave portion of the plate 10. In this state, as shown in FIG. 2C, a pad 13 is pressed onto the plate 10. The pad 13 is made of silicone rubber and might have any suitable shape, such as a semi-cylindrical shape as shown in FIG. 3, a cone shape as shown in FIG. 4 or a shape of frustum of quadrangular pyramid (its upper surface portion has a circular shape). Each of the pads 13 shown in FIGS. 3 to 5 is shaped so as to have a stepped portion at its tip end center portion.
Such pad 13 is pressed to the plate 10 with strong pressure to transfer the ink 11 on the plate 10 onto the pad 13 side as shown in FIG. 2D. Specifically, the pad 13 receives the ink 11. As shown in FIG. 2E, the pad 13, which received the ink 11 from the plate 10, is pressed onto the surface of the cassette housing 2 which is a printed object. Then, as shown in FIG. 2F, the ink 11 is transferred to the surface of the cassette housing 2, and a portion onto which the ink 11 is transferred becomes the print surface 6.
When a very large area is printed by pad printing, an area of the concave portion of the plate also becomes large. Therefore, in the process in which the extra ink 11 is removed by the blade 12, it is frequently observed that the blade 12 sinks deeply in the concave portion of the plate 10 to remove the ink 11 or more than is necessary. As a result, the ink 11 to be transferred to the pad 13 becomes uneven in thickness, resulting in unevenness in the printing.
To prevent the blade 12 from deeply sinking, there is proposed a method in which the plate 10 is shaped in a halftone pattern as shown in FIG. 7 instead of being shaped so as to be a simple concave. The "halftone pattern" referred to in this specification hereinafter represents a pattern in which the whole printing plate is divided in a lattice fashion and a plurality of very small concave portions corresponding to a printed pattern.
A pattern called "150 lines and 90%" is used as the halftone pattern. The pattern is such a pattern that a reference cell 15 having an area of 1/150 square inch, i.e., a section made by dividing a surface of one square inch with 150 lines at constant intervals in each of vertical and horizontal directions is regarded as a reference cell and an area of a concave portion 16 (hatched portion) in the cell 15 occupies 90% of all the area of the cell 15. The rest of 10% is occupied by a convex portion 17 (dotted portion).
As shown in FIG. 9, when the pad printing is carried out with the plate having the halftone pattern thus formed, the pad receives the ink from the concave portion 16 of the plate and transfers it to the cassette housing which is a printed object. Then, since the pad is pressed onto the cassette housing, the ink transferred so as to surround a portion where the ink is not transferred is spread to the portion with on ink corresponding to the convex portion 17 to thereby print the cassette housing in a substantially solid fashion.
As described above, when the tape cassette is printed with the pad printing, the following problems arise.
The above-mentioned pad printing uses the pad of suitable shapes, such as the semicylindrical shape shown in FIG. 3, the cone shape shown in FIG. 4, or the shape of the frustum of a quadrangular pyramid shown in FIG. 5. However, when these pads are used, they are prevented from carrying out the printing using a portion around their tops, so that the printing area is limited. Accordingly, when the label area is provided on the cassette housing in the printing employing the ink on which letters and so on can be written, the label area is limited in shape.
Since the pads having the above-mentioned shapes apply nonuniform pressure to the cassette housing when the cassette housing is printed, it is frequently observed that the cassette housing is cracked.
Especially, since the pad printing cannot provide a sufficient thickness of the ink because the pad printing is transfer printing, a color of the cassette housing cannot be covered satisfactorily. Therefore, in order to cover the color of the cassette housing satisfactorily, the printing is sometimes carried out twice or more on the same surface so as to produce two printed layers or more. In this case, if such printing is continued with the plate having the halftone pattern as shown in FIG. 9, the halftone patterns become overlapped and emphasized when the printing is carried out twice or more although the halftone pattern is not so conspicuous when the printing is carried out once. In that case, the halftone pattern appears as a striped pattern.
It is frequently observed that the print surface is printed on a portion displaced from a correct print position when a printing machine and a plate are not correctly set upon printing. This defect becomes remarkably noticeable especially when a large area up to substantially an outer peripheral portion of the cassette housing is printed like the cassette tape shown in FIG. 1.
Since especially the above-mentioned pad printing is not able to increase the thickness of the print layer to be formed and cannot hide the color of the tape cassette sufficiently, it is frequently observed that the same surface is printed twice or more so as to have two print layers or more in order to remove such disadvantages. In this case, however, the printed layers are displaced in position from each other as shown in FIG. 10, so that this displacement in position leads to difference in covering property, i.e., difference in print density. As a result, an end portion of the print surface looks extremely uneven.
When the ink contains an inorganic filler, the inorganic filler is unsatisfactory in compatibility with an organic material (resin and a solvent) which is a base of the ink, and dispersion, being a factor to lower a material intensity of the print surface. In other words, the inorganic filler is inferior in ink adhesion, wear resistance and scratch resistance of the ink.